Electric Fuel Pump

The fuel pump is an electrical unit, delivering fuel through a pressure regulator, to a fuel distributor or a ring-line for the injection valves. The fuel pump is mounted under the vehicle, near the fuel tank, or in the engine compartment.

Relieve fuel system pressure, as described in this section. Disconnect the negative battery connector. Push back any protective caps and disconnect the electrical connector(s).

If the fuel lines are flexible, pinch them closed with an appropriate tool. Disconnect the fuel lines and plug the ends.

Fig. Fig. 1: Typical 1982-88 fuel supply system

Remove the retaining bolts and remove the pump and expansion tank as an assembly. On the 318i, the pump and mounting bracket come off together. On the 1983-85 733i and 1986 735i, remove the clamp bolt, bend the clamp open, and remove the pump.

The pump can be separated from the expansion tank after removal. On the 318i, separate the pump from the mounting bracket and slide the rubber mounting ring from the pump.

To install:

Fig. Fig. 2: Fuel pump as seen from under the vehicle-1986 3 Series model

Fig. Fig. 3: Clamp off the fuel lines

Fig. Fig. 4: In hard to reach areas, a different type clamp tool may be easier to use

Fig. Fig. 5: Remove the nut securing the fuel pump mount(s)

Fig. Fig. 6: Tag or paint identification marks on the wires to the pump

Fig. Fig. 7: Loosen the clamp(s) securing the fuel line to the pump

Fig. Fig. 8: Slide the hose(s) off the pump assembly

Fig. Fig. 9: Remove the pump assembly from the vehicle

Position the pump in its mounting bracket, sliding the rubber ring around it.

Install the pump to the expansion tank and mount them both as an assembly, connecting the fuel lines.

Connect the electrical leads and the negative battery cable. Run the engine and check for leaks.

1987-88 3 SERIES MODELS

See Figure 10

Relieve fuel system pressure. Disconnect the negative battery connector. Going to the pump, which is under the car and near the fuel tank, push back any protective caps, note the routing and disconnect the electrical connector(s).

Securely clamp the suction hose (coming from the tank) and plug the discharge hose so no fuel can escape.

Fig. Fig. 10: Fuel pump layout-1987-88 3 Series

Open the hose clamp connecting the suction hose to the pump and disconnect it.

Remove the 3 attaching nuts which mount the pump and bracket to the floor pan and remove both as an assembly.

Remove the bolt passing through the 2 parts of the bracket and also mounting the hose attaching strap to the bracket. Then, pull the pump out of the bracket.

Loosen the hose clamp for the discharge hose and disconnect it at the pump. Pull the rubber ring off the pump.

To install:

Note the code number on the pump and make sure to replace it with one of the same number. Inspect all the rubber mounts on the pump mounting bracket and replace any that are cracked or crushed.

Install the pump in the mounting bracket and install the bolt passing through the bracket.

Attach the pump and bracket assembly to the floor pan and secure with the 3 attaching nuts.

Attach all hoses to the pump assembly, make sure to correctly route them. Reconnect the electrical leads.

Run the engine and check all hose connections for leaks.

633CSi, M5 AND M6 MODELS

Relieve fuel system pressure, as described above. Disconnect the battery cables. Working under the fuel tank, pull back the protective caps and then unscrew the attaching nuts and pull off the electrical connections for the fuel pump.

Pinch off the inlet line to the fuel pump and the outlet from the filter. Then, loosen the clamps and disconnect these 2 hoses.

Remove the nut that clamps the fuel line near the pump. Then, remove the 3 bolts which mount the pump and filter to the bottom of the body and remove the assembly.

Remove the bolt fastening the halves of the bracket together and remove the filter from the bracket. Loosen the clamp on the outlet side of the fuel pump and disconnect the line. Then, slide off the rubber bushing in which the pump is mounted.

To install:

Check the code number on the side of the pump and make sure the replacement unit carries the same code.

Install the pump in the mounting bracket and install the bolt passing through the bracket.

Attach the pump and bracket assembly to the floor pan and secure with the 3 attaching nuts.

Attach all hoses to the pump assembly, make sure to correctly route them. Reconnect the electrical leads.

Run the engine and check all hose connections for leaks.

735i MODELS

See Figure 11

The pump on this car is mounted in the top of the fuel tank along with the fuel level sending unit.

If the fuel pump is working well enough to drive the car, run it until the fuel level is as low as possible. If the car cannot be run, devise a safe way to draw fuel out of the tank until the level is low. The best means is some sort of pump and container system designed for this purpose, as siphoning is no longer considered safe because gasoline is a deadly poison.

Relieve fuel system pressure, as described above. Remove the trim panels from the trunk. Then, remove the screws from the cover for the pump/sending unit assembly.

Label the 3 fuel hoses connecting at the top of the pump/sending unit assembly. Unclamp and disconnect the fuel hoses and then plug them.

Fig. Fig. 11: Model 735i in-tank fuel pump system layout

Slide the collar for the electrical connector to one side and then unplug the connector.

Press the 2 retaining locks for the pump unit inward and slide the pump out of the pump/sending unit assembly.

Note the routing of the fuel and electrical lines to the pump from the top of the pump/sending unit assembly. Loosen the 2 hose clamp screws and the screws attaching the electrical connectors to the pump. Disconnect the hose and connector.

Unscrew the pressure regulator from the top of the check valve. Then, unscrew the check valve from the top of the pump.

Pull the insulating sleeve off the pump. Then, loosen the retaining screw and slide the filter off the pump.

To install:

To install the pump, first position the filter on the pump and install the retaining screw.

Install the insulating sleeve to the pump. Screw the check valve into the top of the pump and attach the pressure regulator to the pump.

Connect the hose and the electrical leads to the pump. slide the pump into the pump/sending unit assembly. Position the sending unit assembly in the tank, using a new gasket, and install the 8 retaining screws.

Connect the plug to the top of the sending unit and connect the fuel hoses.

Install the trim panels in the trunk and install the pump/sending unit cover. Connect the negative battery cable and run the engine. Check for fuel leaks.